In the advent of globalization, information is a fundamental and valuable commodity. Information and intelligence regarding national defense and security comes at an even higher premium.
Intentional detection of a signal or message can be accomplished in military systems that use specially designed electronic support measures (“ESM”) receivers. These ESM receivers are often found in signal intelligence (“SIGINT”) applications. In commercial applications, devices employed by service providers (e.g., spectral monitors, error rate testers, etc.) can be used to detect intrusion on their spectral allocation.
Interception is the measurement of waveform features or parameters useful for classifying/identifying a transmitter and/or the waveform type and/or deriving information useful for denying (e.g., jamming) the communication. Exploitation is processing a signal by an unintended receiver in an attempt to locate the transmitter and/or recover the message content. In the broad literature on covert communications these characteristics as applied to transmitted information signals are referred to as low probability of detection (“LPD”), low probability of intercept (“LPI”), and/or low probability of exploitation (“LPE”) by an unintended receiver.
As is known to those of skill in the art, for an unintended receiver the signal detection process is typically based on an energy threshold. The energy the receiver measures is given by Etot=PavgTxmit. Where under general conditions the power Pavg is the received covert signal power S plus internal receiver noise power N. Hence, Etot=(S+N)Txmit. If the signal power used to communicate is only a small fraction of the receiver noise, S<<N, it is extremely difficult for the unintended receiver to reliably detect the presence of the covert signal because the total energy detected will only be marginally greater than the noise-only (S=0) case.
Blind Source Separation (“BSS”) algorithms are often used, as the name implies, to separate the sources of signals. This can be important for SIGINT and other applications. An important aspect helpful to BSS is determining the number of signals present, known as “signal enumeration”. Signal enumeration also requires detection of signals apart from received noise, whether that noise be white or colored. Such detection and discrimination is made significantly more difficult when low energy signals are used as described above, because the receiver receives the transmitted waveforms along with environmental and random noise. Generally, the noise is white Gaussian noise, color noise, or other interferer signals. Prior art detection and enumeration systems and methods have been inadequate due, in part, to the reception of target signals along with environmental and random noise and the inability of the prior art detection and enumeration systems and methods to distinguish the target signal from the noise.
Embodiments of the present inventive system and method address the above needs while requiring only an extremely low power signal.